I usually don't jump right to the chemicals right away and I'll try to get as much as I can using soap and water. If it's really bad, try soaking it in car wash soap and water for a bit, then while submerged, wipe with a sponge. It seems to get rid of most of it. You could try to clay bar it too (but if you don't have chemicals, I'm assuming you won't have a clay bar?)

P21S Wheel Gel (let it dwell for a while before brushing) and a good wheel brush will help tremendously. If there's still some left afterwards, you may need to clay to remove it all. After that you just need to develop a good Wheel & Tire Detailing routine and it will help keep them looking nice all of the time!